A razor knife is a standard commercial item widely used both by the professional worker as well as the home hobbyist or craftsman. It normally comprises an elongated housing adapted to be held in the hand and provided on one side with a slide button that is connected via internal structure in the knife to a razor blade that can be moved from a back position wholly within the handle housing to a front position projecting partially therefrom. As the razor blades used by such a knife are usually very sharp it is essential to be able to withdraw the blade back into the housing when the knife is not in use to prevent accident and injury.
It is relatively common, however, that the blade is left in the extended or front position by the user. This leaves the dangerously sharp blade projecting and creates a considerable hazard in case the user attempts to place the knife back in his or her pocket or accidentally bumps the projecting blade. The solution of providing an automatic withdraw mechanism which continuously urges the blade backwardly so that the user must clamp the blade against this return force has been deemed unsatisfactory because of the difficulty of holding the blade in the out position while using the knife.